For the purposes of this patent specification, a humid air turbine (HAT) cycle is defined to be a combustion turbine power generation cycle where the waste heat from the expander exhaust and/or any oxidant compressor inter/aftercooler is used to water saturate and superheat the oxidant stream before it is fed to the combustor.
The existing technology relating to integrated gasification humid air turbine and integrated gasification combined cycle power generation processes is disclosed in numerous scientific and patent references.
The background art discloses a general concept of supplying feed to an associated air separation unit by removing a portion of the compressed air from the gas turbine air compressor. U.S. Pat. No. 3,731,495 discloses a process in which the air separation unit feed is obtained from the gas turbine air compressor discharge at an elevated pressure, then cooled and further compressed to between 150 and 400 psia to feed the air separation unit. Similarly, U.S. Pat. No. 4,224,045 discloses a process in which some or all of the compressed air feed to the air separation unit is obtained from the discharge of the gas turbine air compressor at elevated pressure then optionally cooled and expanded or compressed so as to provide feed to the air separation unit at a pressure greater than 85 psia. Other references disclose a similar elevated pressure air extraction from the gas turbine air compressor discharge to different air separation unit cycles; these references include U.S. Pat. No. 5,081,845 and U.S. patent application No. 07/837,786. Finally, U.S. Pat. No. 4,631,914 discloses the extraction of intermediate pressure air from an intermediate stage of the gas turbine compressor of a combustion power generation cycle, however, the extracted air is fed to an intermediate stage in the expansion turbine to generate work and does not involve any integration with an air separation system.
The background art discloses a general concept of returning intermediate pressure waste nitrogen from an associated air separation unit to the gas turbine air compressor. U.K. Pat. No. (GB) 2,067,668 and U.S. Pat. No. 4,297,842 disclose a process which uses atmospheric pressure air separation unit waste nitrogen as a diluent to the oxidant air feed to the gas turbine compressor to reduce NOx generation downstream in the gas turbine combustor.
The background art relating to humid air turbine and humid air turbine-like cycles disclose a type of power plant to which the present invention is particularly applicable. U.S. Pat. No. 5,181,376 discloses a process that uses an oxidant air saturator to provide humid air to both a primary combustor/expansion turbine and a separate moist air expander or additional combustor/expansion turbine. U.S. Pat. No. 4,829,763 and U.K. (GB) 2,153,912 disclose a more definitive humid air turbine cycle with the heat of oxidant air compression recovered by an intercooler and an aftercooler associated with the gas turbine air compressor. U.S. Pat. No. 4,653,268 and U.S. Pat. No. 4,537,023 also disclose process systems where the heat of compression is recovered by water in an intercooler and aftercooler before being sent to an oxidant air saturator to provide humid air to the combustor/expansion turbine.
The background art discloses general concepts relating both to the cooling of the gas turbine combustor, transition piece, and expander and to the injection of waste nitrogen from an air separation unit to the combustor or as quench gas upstream of the gas turbine expander.
The following background ad disclose the use of air separation unit waste nitrogen in, and downstream of, the gas turbine combustor. U.S. Pat. No. 5,081,845 discloses "removing nitrogen gas from the air separation unit and boosting the pressure of at least a portion thereof to a pressure substantially equal to that of the fuel stream for introduction to the gas turbine between its [the gas turbine air] compressor discharge and expander inlet". Rathbone U.S. Pat. No. 4,962,646 discloses a system where, "a stream of nitrogen from the higher pressure rectification column [of the air separation unit] is supplied to one of the combustion chambers and the combustion products at a region upstream of the turbine". U.S. Pat. No. 4,707,994 discloses using, "nitrogen product [from the air separation unit] as secondary cooling gas for quenching of a combustor". U.S. Pat. No. 4,557,735 discloses "waste nitrogen sent to combustion zone" and "waste nitrogen sent to combustion gases prior to expansion through the gas turbine". U.S. Pat. No. 4,019,314 discloses "the improvement which comprises admixing the nitrogen produced during the air separation with the waste gases [combustor exhaust stream] before the expansion of the latter", "the nitrogen is admixed to the waste gases between . . . two expansion stages", and "waste gases are expanded in the first expansion stage to the pressure of the nitrogen leaving the air separation plant". Other background art describing similar use of the waste nitrogen include U.S. Pat. No. 5,080,703, U.S. Pat. No. 5,036,672, U.S. Pat. No. 4,697,415 and U.S. Pat. No. 4,697,413.
The key background art disclosing the integration of the air separation unit waste nitrogen with the hot combustion exhaust gases before expansion are U.S. Pat. No. 4,224,045 and U.S. Pat. No. 3,731,495. U.S. Pat. No. 4,224,045 discloses "compressing at least a portion of the nitrogen-rich gas . . . to pressure at least equal to the . . . ignition pressure, and flowing the compressed nitrogen-rich stream into the combustion stream, upstream of said power turbine [gas turbine expander]" and "at least part of said compressed nitrogen-rich stream is injected into the combustion stream after the . . . ignition". U.S. Pat. No. 3,731,495 discloses heating the air separation unit waste nitrogen, "by appropriate blanketing of the metal [combustion chamber] with nitrogen-rich quench gas, the nitrogen enriched gas temperature entering the expander may be as high as 1650 F" and "injecting relatively cool nitrogen-rich gas into said hot combustion gas in a separate quenching zone to form an intermediate temperature nitrogen-enriched gas mixture at super-atmospheric pressure".
The following background art relates to the cooling of the gas turbine combustor, transition piece, and expander. It should be noted that the simplest standard method for gas turbine expander cooling commonly practiced is diverting a portion of compressed air from the gas turbine air compressor to the combustor, transition piece, and first few stages of the gas turbine expander as flow-through coolant for the system. U.S. Pat. No. 5,160,096 discloses a humid air turbine cycle where humidified air is used as flow-through coolant for the first stationary vanes of the gas turbine expander while compressed air before humidification is used as flow-through coolant for the first stage rotor blades before mixing with the hot exhaust gas for further expansion. U.S. Pat. No. 5,095,693 discloses diverting a side stream from the outlet of the gas turbine compressor, removing some of its thermal energy by indirect heat exchange with the fuel stream, then providing it as a reduced temperature coolant for the gas turbine expander. U.S. Pat. No. 4,571,935 discloses steam extraction from a high pressure steam turbine [usually associated with combined cycle operation] to cool the outer shell and the stationary vanes in the expander. U.S. Pat. No. 4,571,935 also discloses system start up and the benefits of independent control of the gas turbine coolant stream. U.S. Pat. No. 4,338,780 discloses injecting a water spray into some of the gas turbine compressor exhaust to prepare a superior pass-through coolant for the moving blades of the gas turbine expander. U.S. Pat. No. 4,314,442 discloses steam cooling of the expander with a thermal barrier film of steam protecting the expander stationary vanes and rotating blades in a flow-through configuration. U.S. Pat. No. 3,973,396 discloses using an Hilsch tube expander to cool part of the gas turbine air compressor discharge before using an ejector configuration to feed this gas into the main air cooling stream to reduce its average temperature and provide a superior flow-through coolant. U.S. Pat. No. 3,783,614 discloses an elaborate closed loop gas turbine expander cooling system using a fluorocarbon refrigerant.
Finally, EPRI report IE-7300, A Comparison of Humid Air Turbine (HAT) Cycle and Combined Cycle Power Plants, March, 1991 prepared by A.D. Rao et. al. discloses the use of the heat of compression recovered from a stand alone air separation unit aftercooler to heat water to saturate the oxidant stream fed to the gas turbine combustor.